1. Field
The following description relates to recycling technology for recovering useful metals from waste solutions and reusing the recovered metals, and more particularly, to electrowinning technology for recovering useful metals.
2. Description of the Related Art
Generally, useful metals are contained in waste solutions, metal plating waste solutions, or washing water generated in the electronic industry, for example, in a semiconductor fabrication process. In particular, a considerable amount of noble metal is contained in waste solutions or washing water generated in industrial processes that use noble metals. Therefore, such noble metals need to be recovered and reused.
Some of the widely used methods of recovering noble metals from waste solutions or washing water include ion-exchange resin, activated carbon, and electrowinning. Solutions from which useful metals have been recovered are neutralized and then discarded and then recirculated for use.
Of the above recovery methods, electrowinning is a method of depositing a target noble metal on the cathode surface by electrolytic reduction of an aqueous solution or a leach solution containing noble metals. In the electrowinning method, a high-purity metal can be obtained directly from a solution without an intermediate process of producing a crude metal, and a solvent can be regenerated and reused in a leaching process.
Despite these advantages, electrowinning suffers from a low metal recovery rate when the concentration of metal ions in an aqueous solution is low although it is easily applicable when the concentration of metal ions in the aqueous solution is high.
That is, active electrowinning occurs when the concentration of a metal in an aqueous solution is about 30 g/l but is not possible when the concentration of the metal in the aqueous solution is only several g/l. In particular, when metal ions are contained in the aqueous solution at an extremely low concentration of 1 g/l, the speed of the metal ions moving to the cathode surface is very low, unlike when the metal ions are contained at a high concentration. Accordingly, it is not easy to recover the metal.
Various technologies are being developed to increase the rate and amount of electrodeposition in order to recover noble metals from waste solutions containing an extremely low concentration of metal ions. However, no satisfactory results have been obtained.